Regenerated lithium-ion cathode materials having modified surfaces

ABSTRACT

A regenerated cathode active material comprises a core material comprising lithium and a transition metal oxide, the core material having a surface, wherein the core material is a recycled cathode active material. At least two different lithium-ion conducting species are on the surface of the core material, and the at least two different lithium-ion conducting species are selected from AlF 3 , Li 3 PO 4 , and a lithium metal oxide. Another regenerated cathode active material for use in a lithium-ion battery comprises a core material comprising a transition metal oxide and lithium, the core material having a surface, and multiple lithium-ion conducting species on the surface, wherein the core material is a recycled cathode active material.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application patent Ser. No.16/177,040, filed Oct. 31, 2018, the entire disclosure of which ishereby incorporated by reference.

TECHNICAL FIELD

This disclosure relates to regenerated lithium-ion cathode materialshaving modified surfaces enabling reuse of the cathode material.

BACKGROUND

Due to increasing demand of lithium-ion batteries for electric vehicles(EVs) and hybrid electric vehicles (HEV), the lithium-ion battery marketis expected to grow rapidly in the next decade. Valuable metals are usedin the cathode active materials of these batteries. The price of cathodeactive materials has been increasing due to the depletion of resourceslike cobalt, nickel and lithium.

The increased demand of EVs and HEVs will lead to a significant increasein end-of-life (EOL) batteries. Therefore, there is interest inrecycling the material in these EOL batteries. Traditional recyclingtechniques (such as pyro-metallurgy and hydro-metallurgy) use smeltingor leaching processes which eventually result in recovering valuablemetals and materials and the recovered metals can be potentially usedfor resynthesizing new cathode active materials or for other purposes.However, these traditional recycling techniques are neitherenvironmentally friendly nor cost-effective.

SUMMARY

Disclosed herein are embodiments of a regenerated cathode activematerial for use in a lithium-ion battery. The regenerated cathodeactive material comprises a core material comprising lithium and atransition metal oxide, the core material having a surface, wherein thecore material is a recycled cathode active material that has beenre-lithiated. At least two different lithium-ion conducting species areon the surface of the core material. The at least two differentlithium-ion conducting species are selected from AlF₃, Li₃PO₄, and alithium metal oxide.

Another embodiment of a regenerated cathode active material for use in alithium-ion battery comprises a core material comprising a transitionmetal oxide and lithium, the core material having a surface, andmultiple lithium-ion conducting species on the surface, wherein the corematerial is a recycled cathode active material that has beenre-lithiated.

Also disclosed are methods of producing a regenerated cathode activematerial for a lithium ion battery. An exemplary method comprises usinga cathode active material removed from an end-of-life lithium-ionbattery, recycled with a direct recycling process, and re-lithiated. Thecathode active material is comprised of a core material having a surfaceon which organic species and inorganic species exist, the inorganicspecies selected from LiOH, Li₂CO₃, Li₂O and LiF. The cathode activematerial is rinsed with a solvent to remove the organic species from thesurface of the cathode active material. After removing the organicspecies, either the cathode active material is heated to a temperatureof ≥700° C. and ≤1000° C. in a hydrogen atmosphere to convert LiOH toLi₂O and reacted with carbon dioxide at a temperature of ≥400° C. and≤700° C. to convert Li₂O to Li₂CO₃, resulting in the cathode activematerial having Li₂CO₃ and LiF as most or all remaining inorganicspecies, or the LiOH and Li₂O are removed from the surface by dissolvingin water, resulting in the cathode active material having Li₂CO₃ and LiFas most or all remaining inorganic species. The Li₂CO₃ and LiF areconverted to lithium-ion conducting species by reacting with one or moreof aluminum, a metal oxide and a phosphate using a solid-state reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is best understood from the following detaileddescription when read in conjunction with the accompanying drawings. Itis emphasized that, according to common practice, the various featuresof the drawings are not to-scale. On the contrary, the dimensions of thevarious features are arbitrarily expanded or reduced for clarity.

FIG. 1 is a flow diagram of a method of recycling cathode activematerial.

FIG. 2 is a flow diagram of a method of regenerating recycled cathodeactive material as disclosed herein.

FIG. 3 is a cross-sectional schematic of a regenerated cathode activematerial as disclosed herein.

FIG. 4 is a cross-sectional schematic of another regenerated cathodeactive material as disclosed herein.

DETAILED DESCRIPTION

Due to the increasing demand of lithium-ion batteries for HEVs, EVs,consumer electronics, and renewable energy storage systems, it isestimated that more than 340,000 ton/year of spent lithium-ion batteriesneeds to be recycled or properly disposed. Traditional metal recyclingprocesses may produce recycled elemental metals, but such conventionalprocesses are not economical and not environmentally friendly. BecauseEOL batteries from EVs still retain about 80% of their initial capacity,recycling of these materials should be prioritized.

A recycling technique, known as a direct recycling process, offers thepotential for greater environmental and economic savings. Directrecycling produces recycled electrode active materials rather than theelemental metals that are produced by hydro-metallurgy andpyro-metallurgy processes. These recycled electrode materials must befurther processed (i.e., re-lithiated) to reinstate the electrochemicalactivity to produce ready-to-use electrode active materials. A shortannealing process may precede the re-lithiation process to improve thecrystallinity and structural defects of the recycled EOL electrodeactive material.

Electrode active materials recovered by the direct recycling processcontain inorganic and organic chemical species on the surface due tobattery cycling under various conditions and electrolyte decomposition,which are not removed during the direct recycling process. Organic andinorganic chemical species can also be formed due to chemical reactionsthat occur during the recycling process. The current direct recyclingprocess is illustrated in FIG. 1 and involves physical separation of thebattery cell materials in step 10, liberation and sieving of the cathodeand anode materials in step 20, and two stage froth flotation in step 30to separate the cathode material from the anode material. The separatedcathode material is re-lithiated in step 40 for reuse as active cathodematerial. Further, a sintering step 50 may be performed to improve thephysical structure of the material.

The surface impurities or impure surface layers on the electrode activematerial cannot be removed or purified by the current direct recyclingprocess. EOL cathode active material is primarily covered by inorganicspecies such as LiOH, Li₂O, Li₂CO₃, and LiF and organic species such asalkoxides (ROLi), carboxylates (LiO—C═O), alcohols (R—OH), andsemi-organic carbonates (RC(═O)OLi). Typically, inorganic species havevery resistive characteristics, thereby significantly contributing tocell resistance. Organic species can be dissolved or removed by soakingor rinsing with dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), 1,2-dimeth-oxyethane (DME), etc. However,inorganic species cannot be dissolved or removed easily during therecycling process.

These surface impurities or impure surface layers lead to limitedelectrochemical performance compared with a virgin electrode activematerial. The battery cell made by the recycled electrode activematerial shows a very high cell resistance and electrode polarization,thereby diminishing the overall efficiency of the battery when comparedwith a virgin (unused) electrode active material. This makes the use ofrecycled electrode material unappealing.

Proposed herein are recycled electrode active materials having modifiedsurfaces so that battery performance is not a disadvantage when comparedwith virgin electrode active material. In particular, the materials andprocesses herein focus on recycled cathode active material forlithium-ion batteries.

The processes and materials herein convert the inorganic species tospecies that enhance the electrochemical performance of the cathodeactive material. The recycled cathode active material is regenerated orre-functionalized with lithium-conducting species. The regeneratedcathode active material, when used in a battery, compared to recycledcathode active material, reduces cell resistance, has better ratecapability, and has longer-term durability (i.e., cyclability). When theregenerated cathode active material is used in a solid-state battery,interfacial resistance between cathode particles and solid electrolyteparticles is reduced due to the layer of multiple lithium-ion conductorson the regenerated cathode active material. The regenerated cathodeactive material has better surface structure stability due to thesurrounding multiple lithium-ion conductors. The multiple lithium-ionconductors protect the core of the regenerated cathode active materialfrom severe etching/corrosion by the acidic species in the electrolyte,as well as reducing oxidation of the electrolyte at high voltage. Thus,the regenerated cathode active material can be adopted for use inhigh-voltage battery cells. The method of regeneration proposed hereinis environmentally friendly and cost-effective, compared to traditionalrecycling techniques.

As disclosed herein, a regenerated cathode active material for use in alithium-ion battery comprises a core material comprising a transitionmetal oxide and lithium, the core material having a surface, andmultiple lithium-ion conducting species on the surface, wherein the corematerial is a recycled cathode active material that has beenre-lithiated. The core material can be any cathode active material knownto those skilled in the art for use in a lithium-ion battery, such asLiCoO₂, LiMn₂O₄, LiMnO₂, LiNiO₂, LiFePO₄, LiNiCoMnO₂, LiNiCoAlO₂, andLiNi_(0.5)Mn_(1.5)O₄ as non-limiting examples.

An exemplary method of making the regenerated cathode active materialsdisclosed herein is illustrated in FIG. 2. The method 100 is performedon a cathode active material removed from an end-of-life lithium-ionbattery, recycled with a direct recycling process, and re-lithiated, asillustrated in FIG. 1. The cathode active material provided in step 110is comprised of a core material having a surface on which organicspecies and inorganic species exist, the inorganic species selected fromLiOH, Li₂CO₃, Li₂O and LiF. The cathode active material is rinsed with asolvent in step 120 to remove the organic species from the surface ofthe cathode active material.

After removing the organic species, the inorganic species LiOH and Li₂Oare either converted to Li₂CO₃ and LiF in step 130 or removed in step140, leaving only Li₂CO₃ and LiF. Step 130 can be performed by heatingthe cathode active material in step 132 to a temperature of ≥700° C. and≤1000° C. in a hydrogen atmosphere to convert LiOH to Li₂O and thenreacting with carbon dioxide in step 134 at a temperature of ≥400° C.and ≤700° C. to convert Li₂O to Li₂CO₃, resulting in the cathode activematerial having Li₂CO₃ and LiF as most or all remaining inorganicspecies. In step 140, the LiOH and Li₂O can be removed from the surfaceby dissolving in water in step 142, resulting in the cathode activematerial having Li₂CO₃ and LiF as most or all remaining inorganicspecies. The Li₂CO₃ and LiF are converted to lithium-ion conductingspecies in step 150 by reacting with one or more of aluminum, a metaloxide and a phosphate using a solid-state reaction. Step 150 isperformed by selecting one or more of aluminum, the metal oxide and thephosphate as the converting material, forming a mixture by mixing theconverting material with the cathode active material, wherein an amountof the converting material is 1.0 wt % to 5.0 wt % of the cathode activematerial and has a diameter of between 1.0 nm and 100 nm, inclusive andcalcining the mixture at a temperature of between ≥600° C. and ≤1100° C.for a period of time.

FIG. 3 is an example schematic of a regenerated cathode active materialfor use in a lithium-ion battery. The regenerated cathode activematerial 200 comprises a core material 210, shown in cross section,comprising lithium and a transition metal oxide. The core material is arecycled cathode active material that has been re-lithiated, such as thecore of the material resulting from the process in FIG. 1, without thesurface impurities. The core material has a surface 220 on which are atleast two different lithium-ion conducting species 230, 240. The atleast two different lithium-ion conducting species are selected fromAlF₃, Li₃PO₄, and a lithium metal oxide.

The lithium-ion conducting species 230, 240 may cover any portion of thesurface 220 of the core material 210. For example, the lithium-ionconducting species 230, 240 may cover a majority or the surface 210, ormay cover nearly the entire surface 220, creating a so-called coating onthe surface 220. The lithium-ion conducting species 230, 240 can benon-uniformly positioned on the core material 210 such that a portion ofthe surface 220 of the core material 210 is exposed.

The regenerated cathode active material 200 in FIG. 3 is provided forillustrative purposes and is not drawn to scale. The core material 210can have a particle size ranging between 5.0 and 25.0 micron, inclusive,and the lithium-ion conducting species 230, 240 can have a particle sizeranging between 1.0 nm and 100 nm, inclusive.

To produce a regenerated cathode active material 200 having lithium-ionconducting species of AlF₃ and a lithium metal oxide, in step 150, theLiF is reacted with aluminum to produce AlF₃ and the Li₂CO₃ is reactedwith a metal oxide to produce a lithium metal oxide. Examples of metaloxides include SiO₂, Al₂O₃, ZrO₂, or TiO₂ with the respective lithiummetal oxide being Li₄SiO₄, LiAlO₂, Li₂ZrO₃, or Li₂TiO₃.

To produce a regenerated cathode active material 200 having lithium-ionconducting species of AlF₃ and Li₃PO₄ and a lithium metal oxide, in step150, the LiF can be reacted with AlPO₄ to produce AlF₃ and Li₃PO₄ andthe Li₂CO₃ is reacted with a metal oxide to produce a lithium metaloxide. Examples of metal oxides include SiO₂, Al₂O₃, ZrO₂, or TiO₂ withthe respective lithium metal oxide being Li₄SiO₄, LiAlO₂, Li₂ZrO₃, orLi₂TiO₃.

To produce a regenerated cathode active material 200 having lithium-ionconducting species of AlF₃ and Li₃PO₄, in step 150, the LiF and theLi₂CO₃ can be reacted with AlPO₄ to produce AlF₃ and Li₃PO₄.

When removing LiOH and Li₂O from the surface by dissolving in water, asin step 140, rather than converting LiOH and Li₂O to additional LiF andLi₂CO₃ as in step 130, additional surface 220 of the core material 210is exposed. Depending on the amount of LiOH and Li₂O removed, the amountof exposed surface area will vary. To further increase the lithium-ionconduction, the exposed portions of the surface 220 can be coated with alithium-ion conducting material. The additional coating can be amaterial that is the same or different from the lithium-ion conductingspecies. As non-limiting examples, the coating can be Li₄SiO₄, LiAlO₂,Li₂ZrO₃, Li₂TiO₃, AlF₃ and Li₃PO₄.

FIG. 4 is an example schematic of another regenerated cathode activematerial for use in a lithium-ion battery. The regenerated cathodeactive material 300 comprises a core material 310, shown in crosssection, comprising lithium and a transition metal oxide. The corematerial is a recycled cathode active material that has beenre-lithiated, such as the core of the material resulting from theprocess in FIG. 1, without the surface impurities. The core material hasa surface 320 on which are at least two different lithium-ion conductingspecies 330, 340. The at least two different lithium-ion conductingspecies are selected from AlF₃, Li₃PO₄, and a lithium metal oxide. Alithium-ion conducting coating 350 is deposited on the surface 320 wherethere are no lithium-ion conducting species 330, 340.

While the disclosure has been described in connection with certainembodiments, it is to be understood that the disclosure is not to belimited to the disclosed embodiments but, on the contrary, is intendedto cover various modifications and equivalent arrangements includedwithin the scope of the appended claims, which scope is to be accordedthe broadest interpretation so as to encompass all such modificationsand equivalent structures as is permitted under the law.

What is claimed is:
 1. A regenerated cathode active material for use ina lithium-ion battery, the regenerated cathode active materialcomprising: a core material comprising a recycled cathode activematerial comprising a transition metal oxide, the core material having asurface; and multiple lithium-ion conducting species on the surface. 2.The regenerated cathode active material of claim 1, wherein the multiplelithium-ion conducting species are selected from AlF₃, Li₃PO₄, and alithium metal oxide.
 3. The regenerated cathode active material of claim1, wherein the core material further comprises lithium.
 4. Theregenerated cathode active material of claim 3, wherein the corematerial is one or more of LiCoO₂, LiMn₂O₄, LiMnO₂, LiNiO₂, LiFePO₄,LiNiCoMnO₂, LiNiCoAlO₂, and LiNi_(0.5)Mn_(1.5)O₄.
 5. The regeneratedcathode active material of claim 1, wherein the lithium-ion conductingspecies are AlF₃ and Li₃PO₄.
 6. The regenerated cathode active materialof claim 1, wherein the lithium-ion conducting species are AlF₃ and thelithium metal oxide.
 7. The regenerated cathode active material of claim6, wherein the lithium metal oxide is one of Li₄SiO₄, LiAlO₂, Li₂ZrO₃,and Li₂TiO₃.
 8. The regenerated cathode active material of claim 1,wherein the multiple lithium-ion conducting species form a coating onthe core material.
 9. The regenerated cathode active material of claim1, wherein the multiple lithium-ion conducting species are non-uniformlypositioned on the core material such that a portion of the surface ofthe core material is exposed.
 10. The regenerated cathode activematerial of claim 9, wherein the exposed portion of the core materialhas a coating comprising a lithium-ion conducting material.
 11. A methodof producing a regenerated cathode active material for a lithium ionbattery, the method comprising: using cathode active material removedfrom an end-of-life lithium-ion battery and recycled, the cathode activematerial comprised of a core material of a transition metal oxide havinga surface on which organic species and inorganic species exist, theinorganic species selected from LiOH, Li₂CO₃, Li₂O and LiF, rinsing thecathode active material with a solvent to remove the organic speciesfrom the surface of the cathode active material; after removing theorganic species, either: heating the cathode active material to atemperature of ≥700° C. and ≤1000° C. in a hydrogen atmosphere toconvert LiOH to Li₂O; and reacting the cathode active material withcarbon dioxide at a temperature of ≥400° C. and ≤700° C. to convert Li₂Oto Li₂CO₃, resulting in the cathode active material having Li₂CO₃ andLiF as most or all remaining inorganic species, or: removing LiOH andLi₂O from the surface by dissolving in water, resulting in the cathodeactive material having Li₂CO₃ and LiF as most or all remaining inorganicspecies; and converting the Li₂CO₃ and LiF to lithium-ion conductingspecies by reacting with one or more of aluminum, a metal oxide and aphosphate using a solid-state reaction.
 12. The method of claim 11,wherein converting Li₂CO₃ and LiF to lithium-ion conducting speciescomprises reacting the LiF with aluminum to produce AlF₃ and reactingLi₂CO₃ with a metal oxide to produce a lithium metal oxide.
 13. Themethod of claim 12, wherein the metal oxide is SiO₂, Al₂O₃, ZrO₂, orTiO₂ and the lithium metal oxide is Li₄SiO₄, LiAlO₂, Li₂ZrO₃, orLi₂TiO₃, respectively.
 14. The method of claim 11, wherein convertingLi₂CO₃ and LiF to lithium-ion conducting species comprises reacting theLiF with AlPO₄ to produce AlF₃ and Li₃PO₄ and reacting Li₂CO₃ with ametal oxide to produce a lithium metal oxide.
 15. The method of claim14, wherein the metal oxide is SiO₂, Al₂O₃, ZrO₂, or TiO₂ and thelithium metal oxide is Li₄SiO₄, LiAlO₂, Li₂ZrO₃, or Li₂TiO₃,respectively.
 16. The method of claim 11, wherein converting Li₂CO₃ andLiF to lithium-ion conducting species comprises reacting the LiF and theLi₂CO₃ with AlPO₄ to produce AlF₃ and Li₃PO₄.
 17. The method of claim11, wherein the cathode active material after re-lithiation is one ofLiCoO₂, LiMn₂O₄, LiMnO₂, LiNiO₂, LiFePO₄, LiNiCoMnO₂, LiNiCoAlO₂, andLiNi_(0.5)Mn_(1.5)O₄.
 18. The method of claim 11, wherein thesolid-state reaction comprises: select the one or more of aluminum, themetal oxide and the phosphate as the converting material; form a mixtureby mixing the converting material with the cathode active material,wherein an amount of the converting material is 1.0 wt % to 5.0 wt % ofthe cathode active material and has a diameter of between 1.0 nm and 100nm, inclusive; and calcine the mixture at a temperature of between ≥600°C. and ≤1100° C. for a period of time.
 19. The method of claim 11,wherein the lithium-ion conducting species form a coating on the corematerial.
 20. The method of claim 11, wherein, when removing LiOH andLi₂O from the surface by dissolving in water, the surface from which theLiOH and Li₂O are removed is exposed, the method further comprising:coating exposed portions of the surface with a lithium-ion conductingmaterial.